Specifically proposed structures of active matrix light-emitting devices including light-emitting elements differ depending on manufacturers. In general, at least a light-emitting element, a transistor (a switching transistor) that controls input of video signals to pixels, and a transistor (a driving transistor) that controls the value of current supplied to the light-emitting element are provided in each pixel.
When all the transistors in pixels have the same polarity, it is possible to omit some of steps for fabricating the transistors, for example, a step of adding an impurity element imparting one conductivity type to a semiconductor film. Patent Document 1 discloses a light-emitting element type display in which transistors included in pixels are all n-channel transistors.
In an active matrix light-emitting device including light-emitting elements, variation in the threshold voltages of transistors that controls the value of current supplied to the light-emitting elements in accordance with image signals (such transistors are also referred to as driving transistors) is likely to influence the luminance of the light-emitting elements. In order to prevent variation in the threshold voltage from influencing luminance of the light-emitting elements, Patent Document 2 discloses a display device which determines threshold voltage and mobility from a source voltage of a driving transistor and sets a program data signal based on the determined threshold voltage and mobility depending on a display image.